The use of arterial--central venous oxygen differences to calculate cardiac output and oxygen consumption in critically ill surgical patients.

Simultaneous determinations of cardiac output (using the cardiogreen indicator dilution technique) and arterial--central venous oxygen differences [C(a-cv)O2] were obtained in 200 critically ill surgical patients. The average initial values +/- SD included arterial--central venous oxygen differences of 3.6 +/- 1.6 vol%, cardiac index of 3.4 "/- 1.2 liter/min/sq m, and oxygen consumption of 100 ml/min/sqm. As might be expected, low arterial--central venous oxygen differences, especially if less than 2.0 vol%, were associated with high cardiac indices, but the oxygen consumptions were much lower than normal and the mortality rates were increased. The cardiac indices calculated from the C(a-cv)O2 averaged 4.1 liter/min/sq m and correlated rather well with the measured cardiac indices, particularly if the patients with a C(a-cv)O2 of less than 2.0 vol% were excluded. Arterial pH values did not correlate well with the calculated oxygen consumption. Arterial oxygen contents of more than 16.2 vol% equivalent to a hemoglobin of 12.5 gm/dl or higher with an oxygen saturation of 95%, provided better arteriovenous oxygen differences, oxygen consumptions, and survival rates than those found with lower hemoglobin values. Arterial--central venous oxygen differences and calculated oxygen consumptions can be practical clinical and prognostic value.